This invention relates to papermaking machines, and more particularly to the covers used on suction boxes in contact with the felts in papermaking machines.
The felts used, for example, in the press section of papermaking machines are critical to proper dewatering of the paper web. These felts are an expensive component of the machine and downtime for replacement results in costly lost production; therefore, it is very important to extend their usable lives as much as possible. In a typical installation, a felt is formed as an endless loop (with or without a transverse seam). A portion of the length of this loop is in contact with one surface of the paper web between the upstream Fourdrinier wire section of the papermaking machine and the downstream dryer section of the machine. The paper and felt are passed through the nip between a pair of press rolls in order to transfer moisture from the paper web to the felt. The paper is then separated from the felt and continues on, while the felt returns in its endless loop. To prepare the felt to again contact the paper web the felt is typically subjected to a high pressure liquid cleaning shower, followed by passage over one or more suction boxes in order to remove liquid and contaminants from the felt and thereby dry it. The typical suction box has a stationary cover over which the felt is pulled at high speed. Slots or other apertures in the cover communicate the reduced pressure inside the suction box to one side of the felt, thereby pulling the felt firmly against the suction box cover. This firm contact between the felt and the suction box cover can cause the cover to wear the felt, thereby shortening the felt's life.
In view of the foregoing, it is an object of this invention to provide improved suction box covers.
It is a more particular object of this invention to provide suction box covers which reduce the wear on papermaking machine felts in contact with those covers.